1. Field of the Invention
In at least one aspect, the present invention relates to methods of optimizing a painting process by establishing a functional relationship between paint process parameters and the resulting paint layer using neural networks.
2. Background Art
The process of painting a vehicle body on a moving conveyor line is extremely complex. The number of possible factors that effect the overall process (inputs) and the number of measurable characteristics of the paint finish (outputs) are in the range of thousands. Furthermore, this high volume/large scale process is under considerable disturbances (variations in environmental parameters, paint parameters, and equipment). The lack of reasonable quantitative description of the relationship between the main components of this complex system has led to development of local controls that only control individual sub-systems or groups of process variables rather than the overall process. Modern automotive paint process controls have partially overcome the inertia of sub-system-based thinking and offer more global control mechanisms that open the door to control and optimization of the entire automotive paint process.
Paint control systems have been developed to control the air flow in the paint booth (i.e., an Air Flow Paint Booth Control System) and to control the quality of the paint layer applied to a vehicle (i.e., an Integrated Paint Quality Control System.) U.S. Pat. Nos. 6,226,568 and 6,146,264 disclose such air flow booth control systems. The first, the Air Flow Paint Booth Control System, regulates the air flows in the paint booth. Consistent air flow is important to the painting process because it strongly influences the efficiency of the paint application, affects paint quality, and impacts energy consumption, worker health and safety. An automotive paint booth consists of several interconnected rooms (called zones) that form a semi-open environment with a conveyor transporting the vehicle body through the respective zones where different parts of the painting process are performed. Air supplied to the booth through multiple supply fans and ducts is used in the booth to remove paint over spray from the booth. From a system perspective the air flows in the paint booth form a highly coupled multi-variable system. Ford's patented feedback control system uses the air velocity measurements from acoustic anemometers to determine changes to control variables (supply fan speeds and/or dampers in the duct work) that regulate the down/cross flows between the process zones.
The Integrated Paint Quality Control System is an automatic spray booth control system that integrates paint automation and paint film thickness measurements into a closed loop feedback control system, which reduces paint process variability and produces consistent, high quality paint finishes. U.S. Pat. No. 6,528,109 discloses such an integrated paint quality control system. Generally, paint film thickness is considered one of the main factors that determine overall paint quality. Surprisingly enough, in a typical paint shop with a high level of control and automation, including dozens of process controllers, PLCs, sensors, robotic devices, automated applicators, etc., the film thickness is measured occasionally on 2–3 vehicles per shift. Evidently, this data is not enough to control and optimize process performance taking into account the variety of possible combinations of colors, styles, and spray booths. In addition, process data is spread out on different systems in the paint shop that makes it hard to correlate process parameters to the resulting paint quality. As a result of this, decisions for determining applicator parameters are usually late and subjective.
From the discussion above, it is evident that an Air Flow Paint Booth Control System is used to determine the efficiency of utilizing the paint while an Integrated Paint Quality Control System is most closely related to determining the film thickness. Although it may seem plausible that these two systems can be decoupled, in reality, such decoupling is rather unrealistic and may lead to an inefficient paint process with an undesirable increase in paint usage. This occurs because the down flows in the spray booth determine a natural film thickness that is a function of the air down flow component for a given flow rate of the paint spray. For higher values of the air downdraft this component may not compensate by manipulating the fluid flows resulting in an essentially uncontrollable overall system. Moreover, it is well known that by properly selecting the airflows the process transfer efficiency can be significantly impacted.
Accordingly, there exists a need in the prior art for improved methods and systems of optimizing paint transfer efficiency while simultaneously improving painting quality control.